1. Field of the Invention
The present invention relates to de-aeration of hydraulic fluid within a reservoir, and more specifically to de-aeration of hydraulic fluid from a return line filter within a reservoir.
2. Background Information
Hydraulic reservoirs are used to hold hydraulic fluid that can be utilized by hydraulic systems, such as used in heavy machinery, including cranes, backhoes, demolition shears, bulldozers, and the like. Within the meaning of this application hydraulic fluid will be inclusive of hydraulic fluid and oil, synthetic oil, bio-fuels, and fuels, which are sometimes collectively referred to as industrial fluids. In hydraulic systems, it is important to keep the hydraulic fluid free of debris. Consequently, filter units or filter assemblies have been incorporated in the hydraulic systems to filter debris from the hydraulic fluid.
U.S. Pat. Nos. 6,116,454; 6,475,380, 6,508,271 and 7,252,759 disclose hydraulic reservoir designs that incorporate specific filter assemblies therein (i.e. in-tank filter elements), and these patents are incorporated herein by reference. The filter elements can be on the outlet lines, as shown in the '454 patent or in the inlet lines as shown in the '380 and '271 patents. A filter element on the outlet or suction side of a hydraulic reservoir is generally a simple strainer. Placing the filter element in the inlet or return lines that extends to the reservoir, as shown in the '271, '380 and '759 patents provides certain advantages relating to the energy required by filtration and returning of the fluid to the reservoir.
The large majority of in-tank filter elements for hydraulic reservoirs utilize a return line filter element of some kind. One known or common example is a forming a partition or separate bowl structure within the hydraulic reservoir and incorporating a top mounted, or drop-in, filter element therein. A similar known configuration is to have the filter element as part of a larger filter assembly with integrated bowl which is “dropped” into the top of the container with the return lines connected directly to the head of the filter assembly. This filter element is also a top mounted structure. The term “top mounted” refers to access or mounting direction in that the filter element is accessed and replaced through the top of the reservoir, such as in the '271 and '759 patents.
Air is detrimental to hydraulic systems because it can cause numerous problems, including Reduced Thermal Conductivity, Higher Oil and Hydraulic Fluid Temperatures, Oil and Hydraulic Fluid Deterioration, Reduced Hydraulic Fluid and Oil Lubricity, Cavitation, Higher Noise Levels, Reduced Bulk Modulus (Increased Compressibility), Reduced Component Efficiency, and Reduced Dielectric Properties.
With new government regulations and other manufacturing pressures, many equipment manufacturers are decreasing hydraulic fluid reservoir sizes to save space & weight. It can be more difficult for air to dissipate from hydraulic fluid with the resulting reduced surface area in the smaller fluid reservoir sizes. Further space restrictions may not allow the reservoir shape itself to be optimized for de-aeration of the fluid.
The prior art fails to adequately provide de-aeration of hydraulic fluid from a filter bowl in a hydraulic fluid reservoir, particularly in a reservoir of reduced size. It is an object of the present invention to overcome the drawbacks of the prior art and to provide an apparatus which de-aerates hydraulic fluid within a reservoir. It is a further object of the present invention to provide a de-aeration design that can be incorporated into the filter bowl and/or the filter assembly design, or alternatively, added as an accessory to an existing filter bowl.